Keyboard pushbutton return spring



Nov. 18, 1969 J. T. LINKER KEYBOARD PUSHBUTTON RETURN SPRING 2 Sheets-Sheet 1 Filed July 19, 1967 J. T. LINKER Nov. 18, 1969 KEYBOARD PUSHBUTTON RETURN SPRING 2 Sheets-Sheet 2 Filed July 19, 1967 BY JJHA/ 7 m2 XZ A26 TTUEA/Fy United States Patent O- US. Cl. 197-98 6 Claims ABSTRACT OF THE DISCLOSURE A positive action tactile pushbutton and combined return spring is disclosed which is constructed of a resilient material having a base including an aperture and a generally frusto-conically shaped tubular protrusion integrally constructed with and extending away from the base coaxially with the aperture. An end of the protrusion is cylindrical and engages a plunger which is manually operated. Upon depression of the plunger with force slightly in excess of a breakover amount, a positive snap action is sensed. Upon release of the plunger the return spring snaps back to its original position thereby returning the plunger to its normally nonoperated position.

CROSS-REFERENCE TO RELATED APPLICATION This patent application is related to the commonly owned co-pending patent application bearing Ser. No. 481,602 and filed on Aug. 23, 1965.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to springs for yieldingly mounting keys of a keyboard in a returnably depressible position. More particularly, this invention relates to keyboard springs which are constructed of a resilient material placed on top of a keyboard and slipped over ends of plungers used to actuate an encoding or other similar device.

Description of the prior art Manually operated encoding devices have many uses in the fields of information transmission and data processing. Commonly alphanumeric characters, or other symbols to be encoded, are inscribed on individual keys of a keyboard as on a conventional typewriter. For any key depressed, an appropriate digital code representative of the selected character is provided at an output for entry into a computer or for transmission to another location as with teletype messages.

Such keyboard encoding devices operate on a variety of principals. For example, they employ mechanical switching arrangements, electronic circuits and, more recently, optical switching devices. One optical device as disclosed in the above referred to co-pending patent application, includes a plurality of keys with each key adapted to be manually depressed when a particular signal is to be encoded. After the depressed key is released, a return force is available to return the key to its original position. Since each key must operate independently from all the others, an independent return force for each key is necessary. As is commonly the case, each key is individually provided with a separate spring which is compressed upon actuation of the key and which returns the key after the operator releases it.

Furthermore, separate components are generally required to serve as tactile response devices which present a snap action upon full depression of a given key. The relatively large number of keys per encoder makes these prior art arrangements bulky and complicated to construct. This results in relatively high costs because of the large num- 3,478,857 Patented Nov. 18, 1969 her of parts and because of time-consuming assembly and repair operations. When repairs are necessary they are expensive, and in addition take the encoding device on which the keyboard is being used out of operation during disassembly and repair.

Spring arrangements for returning the keys to their original position further require frequent cleaning and oiling of the mechanism. To reduce or eliminate this tedious maintenance work, keys have been provided with sealing devices to shield the mechanism from moisture dust and other foreign particles. These sealing devices thus constitute still further additional parts, most commonly in the form of rubber cups or seal rings which are applied to each key. The additional parts, of course, further contribute to the relatively high cost of presently available manually operated keyboards. In addition, such sealing arrangements frequently make it more cumbersome to enter the actuating mechanism when it needs repair or maintenance work.

SUMMARY OF THE INVENTION Briefly, the present invention provides a combined tactile response mechanism and a return spring constructed integrally in a scalable form from a resilient and preferably elastomeric material for use in conjunction with pushbuttons of a keyboard. The keyboard spring includes a substantially planar base provided with an aperture and a first large cylindrical tubular portion having an axis substantially transverse to the base. The first portion extends away from the base coaxially with the aperture. The first tubular portion and the base are integrally constructed and the first portion is further integrally constructed with a second small cylindrical tubular portion. The second portion is coaxially joined to the first portion by a conical transitional section intermediate the first and second tubular portions.

A plunger, which is preferably provided with a cylindrical shaft extending above the keyboard, is disposed within the second tubular portion of the return spring. Upon being manually depressed by an operator the plunger moves axially into the keyboard of the encoding device where it serves in the process of originating the desired output signal. Annular undercuts at the junction of the conical and tubular portions are provided, which undercuts facilitate the depression and return spring action of the keyboard spring. The axial movement of the plunger causes the normally conical portion of the return spring to flatten out, thus increasing the diameter of the first tubular portion. Depressible movement of the plunger creates a force which resists the movement imparted to the plunger by the operator. The resisting force increases with continued movement of the plunger until the normally conical portion has flattened into a substantial plane surface which is approximately level with the expanded diameter of the junction located between the first cylindrical portion and the conical portion of the return spring. At that point an equilibrium in operating and resisting forces is reached. Any further force applied to the plunger results in a snap action wherein the resisting force decreases rapidly as the flattened center portion becomes an inverted cone. Positive actuation of the plunger and the encoding device are selected to coincide with this snap action so that the operator knows that the plunger has moved completely into its signalling position. Upon release of the plunger, a return force, resulting from the increased diameter of the first cylindrical portion tending to restore itself to its normal diameter, returns the inverted conical portion to its normal relaxed shape, thus, lifting the plunger and pushbutton key back to its original nondepressed position. a

Preferably, a plurality of such springs are integrally formed as extensions from a single planar base. The plurality of such springs correspond to a plurality of actuating keys on the keyboard. The planar base together with the keyboard springs are molded in a waffle-like sheet form whereby the manufacturing costs for the keyboard springs are kept to a minimum.

During assembly, the molding is placed on top of the keyboard with the plungers extended through the apertures of the second cylindrical portions of each spring.

The operation is quickly performed and requires no skill and no special tools. This substantially reduces the heretofore high assembly costs.

The inside diameter of the second cylindrical portion of each spring is selected to snugly and firmly seat around an upper end of each plunger so as to establish a seal between the interior of the encoding device and the surrounding atmosphere. This seal does not require the installation of additional parts and is obtained without complicating the construction of the keyboard and/or adding to its cost.

Preferably, the springs and the plungers are adapted to be preloaded such that the amount of travel to actuate the encoding device and the original force required to depress each key can be varied according to the needs of a particular application.

Where the keyboard springs are used in conjunction with other electronic devices which may be sensitive to radio frequency noises and interferences, the return spring molding can be coated with a thin layer of shielding material such as Mu-metal. This shielding serves to protect the encoding device from exterior radio frequency signals, and serves as well, to prevent radio frequency interference signals which may originate in it, from being emitted by the encoding device. The latter problem is frequently encountered in todays aircraft which use a number of radio frequency sensitive instruments.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is an elevational perspective view of an encoding device having a keyboard and keyboard springs constructed according to the present invention;

FIGURE 2 is an elevational view in section of a keyboard spring constructed according to this invention and showing its depressed position in phantom lines; and

FIGURE 3 is an elevational view in section of a modified version of the keyboard spring which shows a nondepressed position of a preloaded spring in phantom lines.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Initially referring to FIGURE 1, an encoding device is shown comprising a housing 12 and an upper face 14 which receives a plurality of keys 16. The keys are preferably designated with alphanumeric characters (not shown) corresponding to a code selected by an operator of the device. A mechanism (not shown) for generating corresponding outputs in accordance with each particular key is enclosed within housing 12 and is not further described since it forms no part of this invention.

The keys are preferably arranged in rows or banks 18 similar to the manner in which conventional typewriter keys are arranged. Each key is mounted on an upper end 20 of a preferably cylindrical plunger 22 (FIGURE 2). Upon being depressed by an operator, the plunger moves axially into the housing, and the encoding device generates an output signal corresponding to the particular plunger having been depressed. After the operator releases the key and therewith the plunger, keyboard spring 24 (FIGURE 2) disposed around the upper end 20 of plunger 22 returns the plunger and the key to their original position.

Referring now in more detail to FIGURE 2, a keyboard spring 24 comprises a first large cylindrical tubular portion 28 which extends transversely away from the planar base 26 and which is coaxial with an aperture in the base 26. Joined to an end 32 of the first tubular portion 28 remote from base 26 is a conical tubular center portion 34 which terminates at its upper end in a second small cylindrical tubular portion 36. The second cylindrical portion is also coaxial with the aperture 30 in base 26 and is provided with an inner diameter which may secure the spring 24 to the upper portion 20 of plunger 22.

The portion 34 has, in its normal non-depressed position, a frusto-conical shape. The large base of the conical portion 34 has an outer diameter equal and integral with the outer diameter of the first cylindrical portion 28. The small base of the conical portion 34 has an outer diameter about equal to the outer diameter of the second cylindrical portion 36. Conical portion 34 may either have a uniform wall thickness, or it may have a wall thickness which tapers from its thicker end adjacent portion 36 to its thinner end adjacent the first portion 28. In either event, first and second annular undercuts 38 and 40 are positioned at the first and second junctions 32 and 33 located intermediate portion 34 and cylindrical portions 28 and 36 respectively. I

The undercuts 38 and 40 are provided to facilitate the ease with which the plunger 22 may be depressed and to assure a positive snap action as it is moved axially in a direction toward the base 26. If the annular undercuts were not provided, depression of plunger 22 might result in unpredictable shapes being assumed in spring 24 thus impairing the ease with which it is deflected and also impairing or eliminating the desired snap and return action which is characteristic of this invention. The upper undercut 40 ensures that cylindrical portion 36 is disposed downwardly toward the base even if the plunger were depressed by eccentric loading. The lower undercut 38 ensures that conical portion 34 tends to flatten out and produce an outwardly directed radial force on the upper part of cylindrical portion 28 as plunger 22 is depressed responsive to a compressive force exerted by the operator. This lower undercut 38 further provides a space which tends to transfer the resistance of the resilient material to an increase in its diameter to a slightly downwardly and inwardly directed radial force at the breakover point. A desirable snap occurs at this breakover point as described further hereinafter. The snap action is further enhanced by tapering the wall thickness of conical portion 34 in the manner shown in FIGURE 2.

The upper end 20 of plunger 22 is preferably provided with an annular protrusion 42 which is disposed above the uppermost end 44 of the cylindrical portion 36. The key 16 includes an internal stepped cylindrical bore 46 and an annular recess 48 capable of engaging the protrusion 42. The key 16, which may be constructed of a substantially rigid material such as plastic, is adapted to be slipped over the upper end of the plunger 22 until the protrusion 42 is securely disposed within the recess 48. The ends of the annular protrusion 42 may be spaced apart to leave a gap 50 intermediate the ends so as to relieve high pressure when the key is slipped over the plunger and to facilitate the installation and removal of the plunger.

The outer step portion of the internal bore 46 has a diameter substantially equal to the outer diameter of cylindrical portion 36. Upon installation of key 16 on plunger 22, an environmental seal is thereby established for spring 24 at cylindrical portion 36 and the top of plunger 22.

Reference to FIGURE 1 shows that the outer perimeter of base 26 may be similarly sealed by cover 14. Thus, the interior components of the encoding device 10 are simply and effectively shielded from contamination by dust, foreign liquids or particles and fromatmospheric humidity.

The tactile snap action and the return spring features of the keyboard spring 24 will now be described by assuming that key 16 (FIGURE 2) is depressed by an operator. As plunger 22 and key 16 move downwardly in an axial direction into the body of the encoding device a compressive force is exerted on the second cylindrical portion 36 to move it downwardly and to transfer the operators force to the conical portion 34. As a result, conical portion 34 is deformed both outwardly and downwardly. At the same time the first cylindrical portion 28 is deformed substantially outwardly at junction 32. This deformation results in a gradually increasing force which opposes further movement of the plunger until a point is reached where the lower junction 33 is about horizontal with the upper junction 32. At this point, referred to as a b reakover point, conical portion 34 has assumed a substantially fiat and horizontal shape; that is, the frusto-conical portion has then assumed a planar deformed configuration intermediate the states shown in FIGURES 2 and 3. Any further downward movement of the plunger results in a breakover wherein conical portion 34 is deflected downwardly to form an annular groove. By virtue of the annular undercuts 38 and 40 this breakover motion is substantially instantaneous since the undercuts and the tapered walls of the center portion tend to prevent the accumulation of any material in the transitional sections which would impair the breakover motion, and further tend to transfer the diameters radial opposition to change into a downwardly directed force which is additive to that of the operators. The substantially instantaneous breakover thus substantially reduces the upwardly acting opposing force exerted onto the plunger, and a snap action is thereby effected. The terminal point of the plungers axial movement into the body of the encoding device 10 is arranged to coincide with a position slightly downward from the breakover point for spring 24. Thus, when a snap action is sensed by the operator he is assured that the lower limit of the plungers axial travel has been reached. This lower limit may conveniently be established by any conventional limit stops known to the prior art.

In the depressed position of the plunger, which is indicated in FIGURE 2 in phantom lines, a return spring action takes place when the operator releases the plunger. As described above, at the breakover point, the resisting force on the plunger decreases markedly from that just prior to breakover. This lesser resisting force, however, is sufficiently strong to push inwardly on the'deformed conical section 34 thus snapping it upward to its normal conical shape. Accordingly, the plunger and key are quickly returned to their original position upon removal of the depression force by the operator.

The amount of force necessary for a snap action together with that exhibited by the return spring can be readily adjusted in accordance with any particular application. For example, the spring material can be selected from many suitable materials having different degrees of resiliency. Further, if the spring material is constructed of natural or synthetic rubber, well known widely available additives can be added to the rubber compound to increase its durometer hardness. With increased hardness, its resistance against deflection is proportionately increased.

In addition, the physical characteristics of the return spring can be suitably changed. For example, the relative diameters of the first and second cylindrical portions 28 and 36 can be varied. Although the outer diameter of the second portion 36 must be less than the inner diameter of the first portion 28 to permit the center portion to enter the space between the first portion and the plunger,'the diameter of the second portion can be increased whereby the resisting force exerted by the spring is decreased. In addition, wall thicknesses can be altered to change the force relations for the spring.

The spring 24 can further be preloaded or prestressed as shown in phantom lines in FIGURE 3. To prestress the return spring, either a key 16 (FIGURE 2) or the annular protrusion 54 is positioned such that when the plunger is in its normally non-depressed position, there is some predetermined interference between the plungers position and the upper end 52 of the second cylindrical portion 36. The spring is thereby deflected downwardly as shown in phantom lines in FIGURE 3 for its normal non-depressed condition. This not only reduces the travel required by the plunger to cause the encoding device to generate an output signal, but it additionally increases the initial force that must be exerted upon the plunger to commence its axial movement into the housing of the encoding device. This is frequently desirable where light objects can come in contact with the keys of the encoding device. These light objects, although not capable of fully depressing the key, may nevertheless partially depress the plunger, which might cause interference signals or misreadings in the encoding device. If the return spring is prestressed, the initial amount of force required to move a plunger is greater whereby the danger of accidental movements of the plungers is reduced.

The springs 24, of which one bank 18 is shown in FIG- URE 1 without any keys 16 in place, are around each plunger of the encoding device and are preferably constructed by molding. As described earlier, this technique permits a high volume production at minimal manufacturing costs since each mold is provided with a plurality of springs which corresponds to the plurality of plungers 22 exposed at the upper face 14 of the encoding device. Aside from its low manufacturing costs, this technique permits a quick assembly of the plungers and the return springs. The molding, comprising the base 26 and the plurality of return springs 24, is simply placed over the ends 20 of the plungers 22 protruding beyond the upper face 14 of the encoding device. It is then pushed downwardly until the base 26 rests against the upper mounting face 14. Thereafter the keys 16 are slipped over the upper ends of the plungers and the device is ready for use.

Should the encoding device be of a type that either emits radio frequency signals or is susceptible to such signals,

the container 12 may be suitably shielded in any Wellknown manner. In accordance with this invention, the upper surface of the base 26 as well as the outer surface of the springs 24 are preferably coated with a thin layer of shielding such as Mu-metal. The coating need be only a few mils thick for adequate shielding. This coating effectively shields the encoding device 10 from radio frequency signals, and does not in any way impair the operation of the springs 24. The area surrounding the keyboard can thereby be completely shielded which was heretofore difficult, especially in cases where the individual keys were provided with a linkage and spring arrangement to return them to their original position. Moreover, the cost of providing this shielding is minimal in comparison with other prior art arrangements.

It is to be understood that the foregoing features and principles of this invention are merely descriptive, and that many departures and variations thereof are possible by those skilled in the art, without departing from the spirit and scope of this invention.

What is claimed is:

1. A return spring for biasing a pushbutton supporting plunger away from a guide base relative to which the plunger is movable along a line substantially normal to the base, the spring comprising a tubular element fabricated of a resilient elastomeric material, the element being arranged for disposition coaxially of the plunger between the base and the pushbutton and normally configured to define first and second opposite coaxially aligned terminal cylindrical portions and a central frusto-conical portion integrally connected circumferentially of its opposite ends with the adjacent ends of the first and second cylindrical portions respectively, the first cylindrical portion having an inner diameter sized to mate with the plunger adjacent the pushbutton end thereof, the inner diameter of the second cylindrical portion being greater than the outer diameter of the first cylindrical portion, the second cylindrical portion being arranged for support by the base circumferentially of the plunger and having suflicient length that the end thereof connected to said frusto-conical portion is deformable radially outwardly to enable said frusto-conical portion to deform into a planar state between said first and second cylindrical portions in response to a compressive load applied axially of the tubular element 'by depression of said plunger, said frusto-conical portion deforming past said planar state with a snap action in response to additional compressive loads.

2. Apparatus according to claim 1 in which the wall of the frusto-conical portion of the element decreases in thickness from the end thereof connected to the first cylindrical portion to the end thereof connected to the second cylindrical portion.

3. Apparatus according to claim 1 wherein the inner surface of the element substantially at the junction of the first cylindrical portion with the frusto-conical portion defines a recess circumferentially of the element thereby to define an annular undercut relative to the inner surfaces of the first cylindrical portion and the frusto-conical portion of the element.

4. Apparatus according to claim 3 wherein the inner surface of the element substantially at the junction of the frustoconical portion and the second cylindrical portion defines a recess circumferentially of the element thereby to define an annular undercut relative to the inner surfaces of the frusto-conical portion and the second cylindrical portion of the element.

5. Apparatus according to claim 1 wherein the end of the second cylindrical portion opposite from the frustoconical portion is joined to a fiat sheet of the resilient material peripherally of an aperture in the sheet.

6. Apparatus according to claim 5 including a plurality of additional tubular elements joined to the sheet and arranged with the one element (i.e., the element described in claim 1) in a predetermined pattern, each of the additional elements disposed peripherally of a corresponding aperture in the sheet and being essentially identical to the one element, the elements being disposed on the sheet so that when the sheet is fiat the axes of the elements are parallel.

References Cited UNITED STATES PATENTS 2,687,015 8/1954 Edwards 7418.2 XR 3,252,342 5/1966 Collins 74-18.2 2,032,168 2/1936 Degen 235- 2,367,441 1/1945 Schwinn 200-168 XR 2,430,064 11/1947 Lawson 7418.2 XR 2,749,757 6/ 1956 Adelt 74-18.2 2,795,144 6/1957 Morse 200168 XR 3,054,879 9/1962 Soreng 200168 XR 3,230,880 1/1966 Beaver 267--1 XR 3,246,112 4/1966 Adams et a1. 200-168 3,315,951 4/1967 Boschi et a1. 267-1 3,317,698 5/ 1967 Mansfield 200-168 3,363,078 1/1968 Ishizaki 74-18.2 XR

FOREIGN PATENTS 553,665 5/1943 England. 352,724 4/ 1961 Switzerland.

OTHER REFERENCES I.B.M. Technical Disclosure Bulletin, vol. 7, No. 12 May 1965, p. 1168, article by R. K. Hayes et a1. entitled Snap-Action Membrane Switch Keyboard.

EDGAR S. BURR, Primary Examiner U.S. Cl. X.R.

Notice of Adverse Decision in Interference In Interference No. 97,761 involving Patent; 3,478,857, J. T. Linker, KEY- BOARD PUSHBUTTON RETURN SPRING, final judgment adverse to the patentee was rendered June 8, 1972, as to claims 1, 2 and 5.

[Ofiicial Gazette August 22,1972] 

